Energetics of burrowing, running, and free‐living in the Namib Desert golden mole ( Eremitalpa namibensis )

Abstract

The Namib Desert golden mole (Eremitalpa granti namibensis) is a small (c. 20 g), blind, sand-swimming, chrysochlorid insectivore that inhabits the sand dunes of one of the driest and least productive areas of the world. Its food, largely termites, is sparse and occurs in widely distributed patches, and free water is unavailable. The moles forage by running on the surface and burrowing below the sand. We estimated their daily energy expenditure in the ®eld to be 11.8 kJ d -1 by constructing a`distance-energy budget' based on measurements of tracks in the sand and the energy cost of running (4.2 kJ d -1 ), burrowing (3.2 kJ d -1 ), and resting (4.4 kJ d -1 ). We also measured ®eld metabolic rate (12.5 kJ d -1 ) and water turnover (2.3 ml d -1 ) independently with doubly-labelled water. The resting metabolic rate (0.5 ml O 2 g -1 h -1 at 35 8C) is about a ®fth of that predicted for a normal insectivorous mammal, and the daily ®eld energy expenditure and water turnover are about a half. The low daily energy expenditure stems mainly from the low resting metabolic rate, which is associated with low body temperatures and metabolic depression. Moles save more energy during foraging by running on the surface of the sand, rather than burrowing under it. The gross energy cost of sand-swimming (80 J m -1 ) is 26 times more expensive than running on the surface (3.0 J m -1 ), but is less than a tenth of the energy required by mammals that tunnel through compact soil. Nevertheless, it would be energetically impossible for the moles to obtain enough food by foraging only underground at our study site. The mean track length was 1.4 km, but only 16 m of it was below the surface. There is evidence that the track length and fraction underground depend on food abundance which is in¯uenced by rainfall.

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

“…Hence, the net cost of transport may depend on soil density, adhesion, moisture content or by thermal balance when an animal digs above thermoneutrality. For a ∼130 g-C. talarum digging in gravelly sand, NCOT is 205 times the prediction for a running mammal of the same body mass (Table 5), but similar to those observed in other subterranean rodents and insectivores (Lovegrove, 1989;Du Toit et al, 1985;Vleck, 1979;Seymour et al, 1998;Kenagy 1987 in Lovegrove, 1989), and 134 times the cost predicted for running tuco-tucos at its maximal locomotor speed (Table 5, Luna and Antinuchi, 2003). NCOT values were different at different T a s, despite the high variance in the burrowing speed observed (Table 5).…”

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

“…Hence, the net cost of transport may depend on soil density, adhesion, moisture content or by thermal balance when an animal digs above thermoneutrality. For a ∼130 g-C. talarum digging in gravelly sand, NCOT is 205 times the prediction for a running mammal of the same body mass (Table 5), but similar to those observed in other subterranean rodents and insectivores (Lovegrove, 1989;Du Toit et al, 1985;Vleck, 1979;Seymour et al, 1998;Kenagy 1987 in Lovegrove, 1989), and 134 times the cost predicted for running tuco-tucos at its maximal locomotor speed (Table 5, Luna and Antinuchi, 2003). NCOT values were different at different T a s, despite the high variance in the burrowing speed observed (Table 5).…”

Thermoregulatory development and behavior of Ctenomys talarum pups during brief repeated postnatal isolation

“…Moreover, as observed in C. talarum, when solitary pups are exposed to temperatures lower than observed in burrows (19 °C), they show a high ΔT b than pups in contact with their mothers and siblings (see Cutrera et al, 2003). Associated with individual or offspring's clustering strategy (Antinuchi et al, 2007), decrease of surfacevolume ratio during periods where pups are isolated is a common behavior within mammals (Seymour et al, 1998).…”

Whole‐body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

“…For example, the blind Namib Desert golden moles ( Eremitalpa granti namibensis ) occupy the least productive terrestrial ecosystem on Earth, searching the sand dunes for patchily distributed insects. They are essentially ectotherms while resting and alert, thermal conforming with metabolic rates about 20% of that expected from other Insectivora (Fielden et al ., 1990; Seymour, Withers & Weathers, 1998). Unlike all other moles that find prey by burrowing, Namib moles find prey by running on the surface, because sand‐swimming is energetically too expensive.…”

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

“…Hence, the net cost of transport may depend on soil density, adhesion, moisture content or by thermal balance when an animal digs above thermoneutrality. For a ∼130 g-C. talarum digging in gravelly sand, NCOT is 205 times the prediction for a running mammal of the same body mass (Table 5), but similar to those observed in other subterranean rodents and insectivores (Lovegrove, 1989;Du Toit et al, 1985;Vleck, 1979;Seymour et al, 1998;Kenagy 1987 in Lovegrove, 1989), and 134 times the cost predicted for running tuco-tucos at its maximal locomotor speed (Table 5, Luna and Antinuchi, 2003). NCOT values were different at different T a s, despite the high variance in the burrowing speed observed (Table 5).…”

Thermoregulatory development and behavior of Ctenomys talarum pups during brief repeated postnatal isolation

“…Moreover, as observed in C. talarum, when solitary pups are exposed to temperatures lower than observed in burrows (19 °C), they show a high ΔT b than pups in contact with their mothers and siblings (see Cutrera et al, 2003). Associated with individual or offspring's clustering strategy (Antinuchi et al, 2007), decrease of surfacevolume ratio during periods where pups are isolated is a common behavior within mammals (Seymour et al, 1998).…”

Whole‐body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

“…For example, the blind Namib Desert golden moles ( Eremitalpa granti namibensis ) occupy the least productive terrestrial ecosystem on Earth, searching the sand dunes for patchily distributed insects. They are essentially ectotherms while resting and alert, thermal conforming with metabolic rates about 20% of that expected from other Insectivora (Fielden et al ., 1990; Seymour, Withers & Weathers, 1998). Unlike all other moles that find prey by burrowing, Namib moles find prey by running on the surface, because sand‐swimming is energetically too expensive.…”

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

“…Hence, the net cost of transport may depend on soil density, adhesion, moisture content or by thermal balance when an animal digs above thermoneutrality. For a ∼130 g-C. talarum digging in gravelly sand, NCOT is 205 times the prediction for a running mammal of the same body mass (Table 5), but similar to those observed in other subterranean rodents and insectivores (Lovegrove, 1989;Du Toit et al, 1985;Vleck, 1979;Seymour et al, 1998;Kenagy 1987 in Lovegrove, 1989), and 134 times the cost predicted for running tuco-tucos at its maximal locomotor speed (Table 5, Luna and Antinuchi, 2003). NCOT values were different at different T a s, despite the high variance in the burrowing speed observed (Table 5).…”

Thermoregulatory development and behavior of Ctenomys talarum pups during brief repeated postnatal isolation

“…Moreover, as observed in C. talarum, when solitary pups are exposed to temperatures lower than observed in burrows (19 °C), they show a high ΔT b than pups in contact with their mothers and siblings (see Cutrera et al, 2003). Associated with individual or offspring's clustering strategy (Antinuchi et al, 2007), decrease of surfacevolume ratio during periods where pups are isolated is a common behavior within mammals (Seymour et al, 1998).…”

Whole‐body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

“…For example, the blind Namib Desert golden moles ( Eremitalpa granti namibensis ) occupy the least productive terrestrial ecosystem on Earth, searching the sand dunes for patchily distributed insects. They are essentially ectotherms while resting and alert, thermal conforming with metabolic rates about 20% of that expected from other Insectivora (Fielden et al ., 1990; Seymour, Withers & Weathers, 1998). Unlike all other moles that find prey by burrowing, Namib moles find prey by running on the surface, because sand‐swimming is energetically too expensive.…”